1. Field of the Invention
The present invention relates to a recording apparatus. More particularly, the invention relates to a recording apparatus used in information processing devices such as a printer, a copying machine, a wordprocessor and a computer.
2. Description of the Related Art
A recording apparatus is known in which a plurality of recording elements such as discharge elements comprising ink discharge ports capable of individually discharging ink droplets, liquid paths and a discharge energy generating element are provided on a recording head at a prescribed fine density to perform recording, corresponding to an arrangement length of the discharge ports, on a recording medium, by means of ink droplets selectively discharged from the ink discharge ports while such a recording head is moved on a carriage in a main scanning direction, and the recording is accomplished by repeating sheet feeding of the recording medium in a sub-scanning direction perpendicular to the main scanning direction.
Recent improvements in the image quality of color ink-jet recorders are remarkable, and further improvement of the image quality to a level known as xe2x80x9cphoto-image qualityxe2x80x9d is now demanded. For the purpose of improving the image quality, there is also an increasing requirement for achieving a higher resolution: while the resolution in the paper feed direction was about 360 dots per inch (dpi) a few years ago, products having a resolution of even 720 dpi are now commercially available.
The distance between adjacent dots, which was 70.6 xcexcm with a resolution of 360 dpi (=25.4 mm/360) is now reduced to 35.2 xcexcm at a resolution of 720 dpi (=25.4 mm/720). In the ink-jet recording method of expressing colors by feeding ink droplets of different colors within a prescribed area, the performance required for the paper feed accuracy is now as high as a xe2x80x9cmicron orderxe2x80x9d.
Three methods for improving the line feed accuracy in the paper feed mechanism in a conventional recording apparatus will now be described.
A first method disclosed in published European Patent document No. 0 680 829 comprises the steps of attaching a rotary encoder on a transporting roller shaft and feeding back information available therefrom, thereby improving the stop position control accuracy.
A second method disclosed in U.S. Pat. No. 5,529,414 comprises the steps of setting the outer periphery length of a transporting roller to N-times a basic amount of line feed, providing a reference position detector for detecting a paper feed starting position of the transporting roller, previously storing correction values for N line feeds corresponding to the amount of eccentricity of the transporting roller, and, when starting paper feed, starting it at the paper feed starting position of the transporting roller without fail.
A third method disclosed in published European Patent document No. 0 760 289 comprises the steps of improving the accuracy of parts related with the paper feed accuracy, and then making adjustments so that the parts accuracy of some parts does not affect the line feed accuracy.
The third method will be described further in detail as being conventional in the art.
FIG. 23 is a perspective view of a transporting mechanism of a typical conventional recording apparatus.
A transporting motor 209, which is a stepping motor, is used as a driving source, and the mechanism has a slow-down gear 210, which is a double gear, and a transporting roller gear 215 directly connected to a transporting roller 211.
FIG. 24 shows a mechanical accuracy table of the transporting mechanism of the conventional recording apparatus. The recording head has a resolution of 720 dpi and has 160 nozzles for each color. Because fine printing is recorded with four passes, the basic amount of line feed would be {fraction (40/720)}-inches or {fraction (1/18)} of an inch. The reduction ratio from a transporting motor gear 216 directly connected to the transporting motor 209 to the transporting roller gear 215 is {fraction (1/24)}, which is achieved through two stages of ⅓ and xe2x85x9. In this configuration, when the outside diameter of the transporting roller 211 is adjusted, and the transporting motor gear 216 makes a turn, the transporting roller 211 feeds a basic amount of line feed of {fraction (1/18)} of an inch.
In the above-mentioned configuration, adjustments are made so that an engagement error of the transporting motor gear 216 or a stop angle error of the transporting motor 209 does not affect the amount of line feed. JGMA class 1 is selected for the slow-down gear 210 and the transporting roller gear 215, and a tolerable error of xc2x110 xcexcm is set for the diameter of the transporting roller 211, and 10 xcexcm for a tolerable deviation.
FIG. 25 is a graph showing calculated values of an error of the paper feed amount in a conventional recording apparatus. The calculation is based on the worst value of the tolerable error of the parts accuracy. Even the largest value is within a range of error of under 10 xcexcm. While this graph contains errors caused by a deviation of the transporting roller 211, an increase or decrease in an average amount of paper feed caused by diameter errors is not included. The calculation is based on the assumption that the average feed amount is an ideal.
FIG. 26 is a graph showing paper feed pitch errors upon a {fraction (1/18)} of an inch feed of the conventional recording apparatus. An average increase in the feed amount caused by a diameter error of the transporting roller 211 is contained. A calculation is made on the assumption of a maximum value of a tolerable diameter error of +10 xcexcm, and an average increase in paper feed amount expected with a feed of {fraction (1/18)} of an inch +1.31 xcexcm is added. As a result, the paper feed pitch error is limited to under 6 xcexcm with a feed of {fraction (1/18)} of an inch.
FIG. 27 is a graph showing a paper feed pitch error upon a line feed of {fraction (1/18)} of an inchxc3x974 in the conventional recording apparatus. In four printing, because the shift of the ink hitting position from printing after four line feeds is a point at issue, this value is important. There is contained an average increase in the feed amount caused by a diameter error of the transporting roller 211. A calculation is performed on the assumption of a maximum value of a tolerable diameter error of +10 xcexcm and there is added an average increase in paper feed amount expected with {fraction (1/18)} of an inchxc3x974 lines +5.24 xcexcm. As a result, it is expected that a paper feed pitch error of about 16 xcexcm would be caused with {fraction (1/18)} of an inch four line feeds.
The conventional recording apparatus has, however, the following problems.
In the first conventional case, the line feed pitch error caused by the amount of transporting roller deviation has not as yet been solved. It is necessary to provide a rotary encoder for each apparatus, thus leading to an increase in cost.
In the second conventional case, the error in stop angle of the transporting motor, and a line feed pitch error caused by engagement error of the transporting motor gear, the slow-down gear, the transporting roller gear and the transporting roller have not as yet been solved. At the start of paper feed, it is necessary to bring the transporting roller back to the starting reference position, and this leads to more complicated control and a disadvantage in improving the recording rate.
In the third conventional case, a higher accuracy is demanded for the slow-down gear, the transporting gear and the transporting roller, resulting in an increase in cost.
An object of the present invention is to provide a recording apparatus permitting improvement of the recording paper line feed pitch accuracy without an increase in cost.
Another object of the invention is to provide a recording apparatus for performing recording onto a recording medium by recording means. The recording apparatus includes transporting means for transporting the recording medium, the transporting means comprising a combination of driving elements including a transporting motor and a transporting roller set so that the other driving elements are reset to an initial state upon completion of a turn of the transporting roller, a detecting section, arranged on the transporting roller, showing a reference position of the transporting roller, a reference position detector detecting the detecting section and outputting a detection signal, a rotation angle measuring device, being detachably attached to the transporting roller, for measuring a rotation angle of the transporting roller, a storage unit previously storing a number of driving pulses for a turn of the transporting roller, corrected so as to provide a constant amount of transportation of the transporting roller, on the basis of information from the rotation angle measuring device for a turn of the transporting roller, and a controller driving-controlling the transporting motor on the basis of the corrected number of driving pulses stored in the storage unit.
It is also an object of the invention to provide such a recording apparatus further comprising a surface height measuring device, being detachably attached to the transporting roller, for measuring a surface height of the transporting roller. In this case, the storage unit previously stores a number of driving pulses for a turn of the transporting roller, corrected so as to provide a constant amount of rotation of the transporting roller, on the basis of information from the rotation angle measuring device and the surface height measuring device and the controller driving-controls the transporting motor, on the basis of the corrected number of driving pulses stored in the storage unit.
It is yet another object of the invention to provide a recording apparatus for performing recording onto a recording medium by recording means. The apparatus includes transporting means for transporting the recording medium, the transporting means comprising a combination of driving elements including a transporting motor and a transporting roller, set so that the other driving elements are reset to an initial state upon completion of a turn of the transporting roller, a detecting section, arranged on the transporting roller, showing a reference position of the transporting roller, a reference position detector detecting the detecting section and outputting a detection signal, a rotation angle measuring device attaching/detaching section, arranged on the transporting roller and being capable of attaching/detaching a rotation angle measuring device, the rotation angle measuring device measuring a rotation angle of the transporting roller, a storage unit previously storing the number of driving pulses for a turn of the transporting roller, corrected so as to provide a constant amount of transportation of the transporting roller, on the basis of information from the rotation angle measuring device, and a controller driving-controlling the transporting motor on the basis of the corrected number of driving pulses stored in the storage unit.
It is a further object of the invention to provide such a recording apparatus further comprising a surface height measuring device attaching/detaching section, arranged on the transporting roller and being capable of attaching/detaching a surface height measuring device, the surface height measuring device measuring the surface height of the transporting roller. In this case, the storage unit previously stores a number of driving pulses for a turn of the transporting roller, corrected so as to provide a constant amount of transportation of the transporting roller, on the basis of information from the rotation angle measuring device and the surface height measuring device, and the controller driving-controls the transporting motor on the basis of the corrected number of driving pulses stored in the storage unit.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings).